1. Field of the Invention
The present invention generally relates to a multi-link variable compression ratio engine. More specifically, the present invention relates to a variable compression ratio mechanism of an engine which uses, non-exclusively, a control shaft, multiple links, a drive motor, and a reduction mechanism to change a top dead center position of a piston.
2. Background Information
A known example of a variable compression ratio mechanism of an engine is one in which a piston and a crank are connected via a plurality of links. For example, in Japanese Laid-Open Patent Application No. 2005-163740, the piston and the crank are connected via an upper link and a lower link, and the compression ratio is variably controlled by controlling the orientation of the lower link. Specifically, the mechanism comprises a control link connected to an eccentric axle provided to a control shaft that is connected at one end to the lower link and extends substantially parallel to the crankshaft at the other end. The orientation of the lower link is controlled via the control link by varying the angle of rotation of the control shaft.
The angle of rotation of the control shaft is controlled by a shaft control mechanism comprising a fork provided integrally to the control shaft, an actuator rod connected to the fork via a connecting pin, and a drive motor for causing the actuator rod to advance and retract in a direction orthogonal to the control shaft.
However, a connection mechanism using a fork (hereinafter referred to as “fork-type connection mechanism”) such as in Japanese Laid-Open Patent Application No. 2005-163740 is configured so that the fork oscillates with bilateral symmetry in relation to the rotational axis of the control shaft, and the reduction ratio between the drive motor and the control shaft varies according to the advanced or retracted position of the actuator rod. In this case, since the reduction ratio is large at a high compression ratio, the control shaft loses responsiveness when the compression ratio is changed from a high compression ratio to an intermediate compression ratio. Therefore, when a sudden acceleration is made from a state having a high compression ratio (for example, a low rotational speed or a low-load operating area), the compression ratio cannot be rapidly changed from the high compression ratio to an intermediate compression ratio, and the problem of more frequent knocking occurs.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved multi-link variable compression ratio engine. This invention addresses this need in the art as well as other needs which will become apparent to those skilled in the art from this disclosure.